As noted in previous chapters, both the laryngeal mask airway (LMA) and the intubating laryngeal mask airway (ILMA) are optimally positioned when lying in the hypopharynx, with the mask atop the glottic opening. This position facilitates passage of a guiding catheter through the tube of the device, often directly into the glottis. An endotracheal tube (ETT) can then be passed over it and into the trachea. The LMA lumen limits the size of the ETT to be passed to a size 6.0-mm internal diameter (ID) in a size 3 or 4 LMA, or a 7.0-mm ID in a size 5 LMA. The 6.0 ETT can project only a short distance past the mask of the LMA, into the larynx, due to the length of these tubes when compared with the length of the LMA itself. In contrast, the ILMA device, in all three sizes, has a lumen large enough to accommodate size 8.0 ETTs. Furthermore, the design of the ILMA and the push rod included with it facilitate removal of the device after the ETT is seated and confirmed to be in the airway.

Anecdotal reports exist that describe the placement of a bougie through an LMA to improve the potential for accurate intubation.¹ However, this technique is probably no better than simply inserting an ETT through the LMA, without guidance,₂ which has a high failure rate.³ These blind techniques are less successful than those that allow visualization of the airway. In a comparison of intubation through the LMA with the use of a bougie versus the ILMA combined with the use of a fiberscope for direct visualization, in patients with inline cervical immobilization, Asai⁴ reported a success rate of 85% for the latter combination but less than 50% for the former.

A technique that has generated more interest, and is likely to improve the accuracy of ETT placement, is the use of a lightwand, placed through an LMA or ILMA device, to allow the practitioner to guide an ETT into the larynx with transillumination. Agro et al made use of this technique in 114 patients under anesthesia, after LMA insertion. After successful LMA placement, the lightwand and ETT were inserted into the LMA, projecting 1.5 cm beyond the grill.⁵ In 78% of patients, the authors were able to intubate without repositioning the LMA, whereas 10% required repositioning, and 9% required a change to different-sized LMA. Three patients were impossible to intubate in this manner.

Nijima et al⁶